(a) Technical Field
The present invention relates to a method of controlling a glow plug, more particularly, to a method of controlling the operation of a glow plug in a hybrid electric vehicle (HEV) equipped with an electric motor and a diesel engine as driving sources of the vehicle.
(b) Description of the Related Art
Automobile engines can be classified into a gasoline engine and a diesel engine.
The gasoline engine, an internal combustion engine using gasoline (volatile oil) as fuel, achieves combustion by taking air and gasoline into a cylinder and igniting the compressed gas mixture.
On the other hand, the diesel engine, an internal combustion engine using diesel (light oil) as fuel, achieves combustion from self-ignition by taking air into a cylinder using a piston, compressing it at high pressure, and then injecting the fuel at high temperature under high pressure.
The diesel engine has higher fuel efficiency than the gasoline engine, so it consumes less fuel, and the operation cost is economical because the fuel is inexpensive. Further, the use range of the fuel is wide, so it can use a substitute fuel such as kerosene, vegetable oil, etc.
It has been studied to equip hybrid vehicles, which use an electric motor and an engine together as driving sources, with a diesel engine instead of a gasoline engine.
The diesel engine, however, has an auxiliary starter called a glow plug that preheats the air in the engine cylinder to make sure of starting the engine in the winter season.
The glow plug, which is provided for heating the air in a cylinder in advance at a high temperature for easy self-ignition of the fuel in a diesel engine, is a heating element driven by electricity and is also an auxiliary starter that is necessary for compressing and igniting the fuel and the air in a cylinder under a low-temperature condition of a diesel engine.
Further, a preheating lamp showing whether the glow plug operates is provided to inform the driver whether the air in a combustion chamber is sufficiently heated.
Since most diesel engine vehicles do not stop the engine when they are running after the engine is started, the glow plug is used only for starting the engine at the beginning.
Further, in diesel engine vehicles with Idle Stop & Go (ISG), idle-stop is performed only when the temperature of the engine is over a predetermined level, so the glow plug is used only for starting the engine at the beginning.
In contrast, in hybrid vehicles equipped with a diesel engine (diesel hybrid vehicles), the engine is frequently turned on/off with driving of the electric motor, and accordingly, the glow plug is used every time the temperature of the cylinder is low to start the engine; therefore, it is required to develop a technology of controlling the glow plug on diesel hybrid vehicles.
In the related art about controlling a glow plug, there are Japanese Patent Registration No. 5333524 and Korean Patent Application Publication No. 2006-0023616, where controlling a glow plug described in those documents are for general engine vehicles and are not suitable for diesel hybrid vehicles of which the engine is frequently turned on/off when they are running.
In preheating control of a glow plug, preheating and the operation time (preheating time and glow plug-on time) are determined in accordance with the coolant temperature and the battery voltage state in an ignition-on state of a diesel engine, or the load of the glow plug is measured and then preheating control is performed, because the load changes with temperature.
In the process of preheating control, whether or not preheating is performed is shown by a preheating lamp that is turned on/off in the shape of a coil on a cluster so that the driver can be informed, where the engine is started when the preheating is finished and the preheating lamp is turned off.
Further, when the engine is started with the preheating lamp on, that is, without completing the preheating by the glow plug, it is impossible to control vibration and engine speed due to incomplete combustion in the engine cylinder when keeping an idle mode after starting the engine.
Further, starting the engine of hybrid vehicles depends on predetermined conditions such as the vehicle speed, driver-required power, and the State of Charge (SOC) of the battery, and particularly, when the driver-required power is over a running-available power (standard power) of an Electric Vehicle (EV), the engine is started.
However, the driver-required power cannot be estimated, so it is impossible to specify the point of time for starting a glow plug in the related art, and accordingly, there was a need of a method of controlling a glow plug and a method of controlling an engine operation mode for diesel hybrid vehicles.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.